1. Field of the Invention
The present invention relates to a fine particulate cross-linked type N-vinylamide resin (i.e., same meaning as N-vinylcarboxylic acid amide resin), a process for producing the same, a microgel composed of the cross-linked type N-vinylamide resin comprising that resin swelled or gelled with water or an organic solvent, and a thickener, dispersion stabilizer, or lubricant comprising that microgel as a main component. More specifically, the present invention relates to a fine particulate cross-linked type N-vinylcarboxylic acid amide resin having an excellent chemical stability and affinity for water and organic solvents such as alcohols, particularly exhibiting a high thickening ability, dispersion stability, and lubricity without being affected by an electrolyte solution in which inorganic or organic ions coexist in the system, a microgel having a wide usage in various fields due to the excellent characteristics and functions of the resin, and a hydrophilic thickener, or a thickener having an additionally added organic solvent affinity dispersion stabilizer, or lubricant comprising the microgel as the main component.
2. Description of the Related Art
In the prior art, fine particles of a cross-linked hydrophilic gel exist as a dispersion of swelled fine particles in water unlike a water-soluble linear polymer which exists as a solution in water. The dispersion thereof exhibits a non-Newtonian flow even at a low concentration and exhibits a remarkably high viscosity, as is widely known in the art. It has been variously utilized as a thickener, dispersion stabilizer, and lubricant for aqueous gel-like products, textile size, and cosmetics.
As the cross-linked type fine particles known in the art, for example, synthetic polymers such as cross-linked type polyacrylic acid (carboxyvinyl polymer) and cross-linked type acrylic acid copolymer may be included. These cross-linked type fine particles, however, are all cross-linked products of the polymeric electrolyte type, and therefore, exhibit an excellent thickening ability for water containing no electrolyte but exhibit only remarkably low thickening ability for an aqueous liquid containing a large amount of organic or inorganic ions, such as a natural extract, surfactant, perfume, colorant, reactive dye for printing, and cement slurry. This is considered to be a result of a reduced expansion of the chains because of a suppression of dissociation of the polymeric electrolyte, which is the backbone chain of the cross-linked product, in the presence of ions. Further, when polyvalent metal ions exist, ion cross-linking occurs through the backbone carboxylic acid, whereby a cross-linked polymer with a substantially higher cross-linking density than required is formed, which lowers the thickening ability.
To overcome the drawback mentioned above, Japanese Unexamined Patent Publication (Kokai) No. 4-323213 discloses a non-ionic thickener substantially free from the effect of electrolytes comprising a fine particulate cross-linked type N-vinylcarboxylic acid amide resin. This thickener is improved in regard to the defect of the above polymeric electrolyte thickener, that is, the reduction of the thickening ability in an electrolyte solution, but since it is non-ionic, requires a larger amount of resin to be added to obtain a high viscosity liquid and therefore causes a drop in the feeling of use in cosmetics etc.
In water absorbing resins known in the art, an aqueous dispersion thereof exhibits viscosity, but because of the greater particle size, the system as a whole becomes non-uniform and therefore does not exhibit a thixotropic viscous behavior.
Further, among natural polymers, such as those which are not fine particles but exhibit a viscous behavior similar to the cross-linked type fine particles, there may be included natural gums such as gum tragacanth, locust bingham, sodium alginate, carrageenan, and guar gum. These natural polymers, although they contain the groups of electrolytes, exhibit a relatively good thickening ability also for an aqueous liquid containing a large amount of ions. Natural polymers, however, not only fluctuate in cost, but also are susceptible to attack by microorganisms, bringing the problem of corruption, and have a peculiar color and odor, thus the scope of use thereof is limited.